1. Field of the Invention
The present invention relates in general to a compact disc (CD) molding apparatus, and more particularly, to a CD molding apparatus with auxiliary gas channels.
2. Description of the Related Art
Compact Disc (CD) advantages of large storage volume, low cost and long-time storage integrity have led to wide application in storage of data such as digital images, music and photos. In the manufacturing process, tiny Polycarbonate (PC) pellets are melted to mold a transparent plastic substrate, subsequently plated with metal by vacuum evaporation or sputtering, forming a reflective layer. Digital data is thus read by laser light reflected via the reflective layer. The metallic reflective layer, while normally aluminum, can also be gold, silver or copper. The CD is finished coating the metallic reflective layer with a protective lacquer.
Referring to FIG. 1, a conventional CD mold apparatus has a fixed mold 1 and a movable mold 2. As shown in FIG. 1, a disc-shaped mold cavity 4 is defined between the fixed mold 1 and the movable mold 2 to mold a substrate, with a stamper 21 fixed on the movable mold 2, having a transfer surface 211 with pit patterns thereon to imprint digital information to the CD substrate. Particularly, the mold 2 is movable perpendicular to the transfer surface 211 such that the CD substrate can be stripped. High temperature gas, generated by melted Polycarbonate (PC) injection in the mold cavity 4 is exhausted through the gas passage 5.
As shown in FIG. 1, to facilitate exhaust flow of the high temperature gas, the fixed mold 1 has several air channels 12 connected to the mold cavity 4 near the central inlet 110 where Polycarbonate (PC) is injected. External air is taken in by an air pump through the air channels 12 into the mold cavity 4 to strip the substrate. High temperature gas in the mold cavity 4 thus passes through the gas passage 5 and exits via outlet 6 as the arrow indicates.
As mentioned above, high speed and high volume air from the channels 12 facilitates exhaust of high temperature gas from the mold cavity 4, however, the CD mold apparatus and transferring surface 211 can be contaminated and damaged by excess gas flow gas choking the gas passage 5.